Electronics: Lesson 012 - Experiment 13: barbecue LED

experiment 13： Barbecue LED

Burn one LED It is very simple . What actually happened was ： Excessive current flows through LED, Generate too much heat , Damaged LED. If the heat generated by the current burns LED, Will the heat generated by the soldering iron have the same effect ？ It seems likely that .

Items needed

• Needle nose pliers 、30 W（ or 40 W） Soldering iron 、15 W Soldering iron
• Auxiliary tool （ For clamping elements ）
• Pure copper spring clip , One big or two small
• 9 V Batteries and connectors , or 9 V communication — DC adapter
• Universal LED 2 individual
• 470 Ω resistor 1 individual

The purpose of this experiment is to study the effect of heat . This means that we need to understand the flow path of heat . therefore , Bread board is not used in this experiment , Because the heat absorbed by the circuit inside the bread board is unknown . I also do not recommend that you use test leads , Because they also absorb heat .

Please use pointed nose pliers to handle LED and 470 Ω Each pin of the resistor is bent into a small hook , Pictured 3-62 Shown ,9 V The connecting wire of the battery is also bent into a hook .

In order to minimize heat loss during conduction , The resistor is suspended in LED On one pin of the , Down a little , The power cord is hung on the pin of the resistor . Gravity is enough to support the system .

Clamp with an auxiliary tool LED Plastic body . Plastic is a poor conductor of heat , therefore LED The body of the device will not allow too much heat to be transmitted through auxiliary tools .

add 9 V voltage ,LED Will shine .

You need to use low power 15 W Soldering iron and high-power soldering iron . Plug in the plug , Wait at least five minutes , Make sure the soldering iron is hot enough .

Now? , hold 15 W The tip of the soldering iron is pressed against the shining LED On one pin of the , At the same time, count the time with a watch . chart 3-63 exhibition
The experimental setup is shown .

I bet you can press for three minutes without burning LED. Now you know , Why do I recommend it 15 W The soldering iron is used for precise electronic work .

Give Way LED The pins of the are cooled for a while , Then press the soldering iron with higher power on the same position . In my submission LED It will go out in ten seconds （ Be careful , There are some LED Can withstand higher temperatures ）. therefore ,30 W Soldering irons are not used for precise electronic work .

The temperature of a high-power soldering iron is not necessarily higher than that of a small soldering iron , It just has a large heat capacity . in other words , It can provide more heat faster .

Yours LED Dedicated to knowledge , It died a glorious death . Let it sleep in the garbage can , Put on a new one LED, This time,
We should treat it more kindly . The connection method remains the same , But this time add a large copper spring clip （ Or two small clips ）,
Clip in LED On a pin near the body , Pictured 3-64 Shown . hold 30 W or 40 W The tip of the soldering iron is pressed under the spring clip
On the pin . This time, , You should be able to heat it with a large soldering iron for two minutes , It will not burn out LED.

Where's the heat

Touch the spring clip after the experiment , You will find it hot , and LED Still not too hot . Imagine , Heat flows from the tip of the soldering iron , Inflow and LED Connected wires —— Unless the heat hits the spring clip on the way , It changes the path , Pictured 3-65 Shown . The spring clip is like an empty container waiting to be filled , The heat prefers to flow into the spring clip , And protection LED flawless and perfect .

The spring clip functions as a radiator . It is better than the commonly used nickel plated steel spring clip , Because copper is a good conductor of heat .
Back to the first part of this experiment , Have you found , Without a radiator ,15 W The soldering iron is not damaged LED. Does this mean
our 15 W Your soldering iron is absolutely safe ？

It is possible . however , You don't necessarily know whether some semiconductor components have higher temperature ratios LED More sensitive .

Because the consequences of burning components are really annoying , So I suggest you take it easy , Use radiators in these cases .

• 15 W The soldering iron is close to the semiconductor component 20 Seconds or more .
• 30 W The soldering iron is within half an inch of the resistor or capacitor 10 Seconds or more .（ Keep away from semiconductor components .）
• 30 W The soldering iron is close to any fusible object 20 Seconds or more . Fusible objects include wire insulation 、 Plastic connectors and plastic components inside switches .

Radiator usage rules

• Large copper spring clips work best , But it may not be suitable for narrow places . You'd better have the small spring clip ready at the same time .
• Clamp the spring clamp as close to the element as possible , As far away from the welding point as possible , Because the weld is really hot . What is to be transferred is the heat of the element , Not the heat of the weld .
• Make sure that... Is formed between the spring clip and the wire Metal ~ Metal Connect , To promote good heat conduction .
  Remember the above , We can continue to challenge the interesting point-to-point wiring .